package cn.kent.high.juc.lock.reentrantLock;

import java.io.Serializable;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * 手写 不可重入锁
 * 思路：通过state变量， ==0 表示可获取状态，==1表示已经有线程获取即不可获取。
 * 因为不可重入，所以不会出现>1的情况。
 */
public class NonReentrantLock implements Lock, Serializable {

    /**
     * 内部帮助类
     */
    private static class Sync extends AbstractQueuedSynchronizer {
        /**
         * 是否锁已经被持有
         */
        @Override
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }

        /**
         * 如果state==0，尝试获取锁
         */
        @Override
        protected boolean tryAcquire(int acquires) {
            assert acquires == 1;
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        /**
         * 尝试释放锁,设置state为0
         */
        @Override
        protected boolean tryRelease(int release) {
            assert release == 1;
            if (getState() == 0)
                throw new IllegalMonitorStateException();
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        /**
         * 提供条件变量接口
         */
        Condition newCondition() {
            return new ConditionObject();
        }
    }

    // 创建一个sync来做具体工作
    private Sync sync = new Sync();

    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }

    @Override
    public void unlock() {
        sync.release(1);
    }

    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }

    public boolean isLocked(){
        return sync.isHeldExclusively();
    }
}
